1. Field of the Invention
The present invention relates generally to a method for recording a video signal at a point just adjacent to the last video frame which was previously recorded, and in particular, to a video tape recording method that is capable of precisely locating the beginning track of the subsequent recording at the contiguous recording portion on the video tape on the subsequent recording by recording a unique position identification code together with every frame of the video signal being recorded and reading out the recorded position identification codes when recording is resumed after the recording is stopped temporarily
2. Brief Description of the Prior Art
FIGS. 1A and 1B show the recording/reproducing portion in the video tape recorder which comprises a key pad 1 for inputting control instruction; a memory 3; a control unit 2 for controlling the recording/reproducing unit; and the a recording/reproducing unit 60. The recording/reproducing unit 60 comprises a capstan motor 5 and a capstan shaft 5xe2x80x2 for driving the video tape; a motor controller 4 for controlling the speed of the capstan motor 5; a pinch roller 7 which pinches the tape to the capstan shaft 5xe2x80x2; a control head 6 which records and reads control pulses in the control track on the tape; the video heads 9xe2x80x2 for recording and reproducing the video signal on the tape; and a rotating drum 9 on which the video heads 9xe2x80x2 are mounted.
In the video tape recorder configured as shown in FIGS. 1A and 1B, the prior art for correctly locating the starting track just adjacent to the last track recorded before the temporary recording stop is as follows. When the video tape is stopped temporarily during the recording operation by a stop instruction through the key pad 1, the control unit 2 blocks the video signal which has been fed to the video heads 9xe2x80x2 and stops the recording immediately by controlling the motor controller 4 (refer to (A) in FIG. 2). After rewinding the video tape for a predetermined time, the control unit 2 remains on hold waiting for the subsequent recording request (refer to (B) in FIG. 2). During the rewinding, the control head 6 reads 30 Hz control pulses that have been recorded on the control track of the tape, and the control unit 2 counts the number of the reproduced control pulses from the control head 6. The counted value is stored in the memory 3. Instead of the control pulses, a capstan frequency signal (CFG) generated by revolution of the capstan motor 5 can be used.
After that, when the recording operation restarts by inputting a stop cancel instruction through the key pad 1, the video tape starts to move in the forward direction in cooperation with the pinch roller 7 and the capstan shaft 5xe2x80x2 without video recording. In this way, the control unit 2 forwards the video tape until the number of control pulses reproduced by the control head 6 is equal to the counted value that is retrieved from the memory 3 (refer to (C) in FIG. 2). Once the video tape is moved by the amount corresponding to the number of the control pulses counted during the rewinding mode, the recording operation is restarted at the location where the recording was temporarily stopped.
For the prior art above, when the video tape moves in the backward direction or in the forward direction (Axe2x86x92B movement in (B) of FIG. 2) by the amount corresponding to the number of control pulses that was counted in the rewinding operation (Bxe2x86x92A movement in (B) of FIG. 2), the tape may not adhere closely to the control head 6 or the pinch roller 7 because of the initial transient travel speed of the tape . Thus, the control pulses often fail to be counted precisely in the reproduction operation (Axe2x86x92B movement in (B) of FIG. 2) or the tape may not move by the amount corresponding the counted CFG pulses. For example, P position in (B) of FIG. 2 is not located precisely, resulting in an abrupt change in spacing such as overlap (FIG. 3A) or wide blank section (FIG. 3B) between the last track of the previous recorded video signal and the beginning track of the subsequent recorded video signal in the contiguous recording portion.
The primary objective of the present invention is to solve the above mentioned problems of the prior methods and to provide a method for continuous video tape recording at the boundary between two video signals recorded during two consecutive record modes by recording position identification codes on the video tape together with video signals and detecting the position identification code thereon.
Another objective of this invention is to provide a method for continuous video tape recording at a contiguous recording portion which can be applied successfully in cases where recording and pause are repeated for a short period of time.
The present invention, a method for continuous video tape recording at a contiguous recording portion, comprises the following steps: generating a unique position identification code for every frame of the video signal to be recorded; summing each of video frames with a signal containing the position identification code and recording the resultant video signal on a video tape; stopping recording of the video signals temporarily and memorizing the position identification code which was recorded on the video tape with the last video frame; and rewinding the video tape for a predetermined period of time.
The method according to the present invention is further characterized in that the value of the position identification code changes in serial order.
If the recording of a video signal is requested by a user, a signal containing a position identification code is superimposed into a particular period within every frame of the video signal and the resulting video signal is recorded on a video tape, the value of the position identification code being changed in serial order. Then, when a temporary recording stop is issued by the user, the recording of the video signal is stopped immediately and at the same time, the position identification code within the last video frame on the tape is memorized. After the tape is rewound by a predetermined amount, it is maintained in a waiting for the subsequent recording. After that, when the temporary recording stop is canceled, the recorded video signal passed by during the rewinding begins to be reproduced. During the reproduction, the unique position identification code is read out from the particular period of every frame of the reproduced video signal and is compared with the memorized position identification code. At the instant the codes coincide each other, the reproduction mode is switched to the recording mode. Thus, the starting track of the subsequent recording is located precisely so that it is closely adjacent to the last track recorded in the preceding recording mode.
Thus, the recording method of the present invention is capable of avoiding overlap and eliminating the blank section between the last track of the preceding recorded video signal and the beginning track of the subsequent recorded video signal, which often arises at the recording joint portion on the tape when the tape is abruptly driven by the initial transient power of a motor on successive operations of recording-and-pause.
Besides a home video tape recorder, the present invention can be applied to a camcorder or a time-lapse video cassette recorder that is used for long-time surveillance or observation.
The above objectives, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to read in conjunction with the accompanying drawings.